One material very commonly selected for large-scale construction projects is reinforced concrete (RC). Several years ago, the Army Corps of Engineers discovered that the use of a modified vitreous enamel improved the bond strength, and, possibly, the corrosion resistance of the steel rods reinforcing the concrete. The enamel consisted of a glass matrix embedded with reactive ceramic particles. The glass composition was designed to strongly adhere to the steel, and the reactive particles were imbedded to chemically react with the surrounding cement to form another strong bond.
The materials used for these initial tests included commercial alkali-resistant groundcoat enamels for steels used in a variety of consumer and industrial applications. The typical compositional ranges for such enamels are summarized below as Table 1.
TABLE 1Compositional ranges for typical alkali-resistant groundcoatsConstituentRange (wt %)Silicon dioxide SiO240-45Boron oxide B2O316-20Na oxide Na2O15-18K oxide K2O2-4Li oxide Li2O1-2Ca oxide CaO3-5Aluminum oxide Al2O33-5Zr oxide ZrO24-6Mn dioxide MnO21-2Ni oxide NiO1-2Cobalt oxide Co3O40.5-1.5Phosphorus oxide P2O50.5-1  
The ratio of the Na2O, B2O3, and SiO2 components, as well as the addition of other alkali (K2O and Li2O) and alkaline earth oxides (CaO), have the greatest effect on the thermal properties of the glass. Constituents like Al2O3 are added to improve the corrosion-resistance of the glass. ZrO2 (and P2O5) is usually added to an enamel as an opacifier to affect the visual appearance of the coating. However, zirconia has the added advantage of improving the chemical resistance of silicate glasses to attack by alkaline environments. Alkaline-resistant silicate glass fibers developed for reinforcing cement composites typically contain 10-20 wt % ZrO2, and a protective coating of Zr-oxyhydroxide forms on the glass surface when exposed to an alkaline environment, further impeding corrosion. Transition metal oxides, like MnO2, CO3O4, and NiO, are added to enamels to aid bonding to the substrate.
In general, these materials are sodium-borosilicate glasses modified with various constituents to tailor thermal and chemical properties. However, the conventional groundcoat enamels (such as the ones listed in Table 1) are designed with thermal properties tailored for the steel alloys used in commercial and industrial applications. Therefore, there is a need to provide a new and improved glass composite having physical and chemical properties specifically suited for coating the reinforcing steel used in RC structures, specifically with thermal properties tailored for steel alloys used in RC structures and with chemical properties designed for alkaline cement environments. There is likewise a need for reinforcing steel members having corrosion resistant coatings better matched to the physical properties of the underlying steel so as to better adhere thereto. Finally, there remains a need for an improved steel-concrete composite material wherein the steel phase is more securely bonded within the concrete matrix phase to yield a tougher composite material. The present novel technology addresses these needs.